PROJECT SUMMARY/ABSTRACT In the United States, hepatocellular carcinoma (HCC) incidence and mortality rates are increasing among the most rapidly of all cancers. Cirrhosis, characterized by long-standing inflammation, is a well-defined pre-cancer lesion, although the transformation from cirrhosis to HCC is poorly understood. Currently, the only clinical option for the increasing, high-risk population of patients with liver cirrhosis is to watch and wait for HCC to develop. Thus, there is an urgent need to identify pathways for the progression of liver cirrhosis to HCC. Experimental data show that perturbations in the gut-liver axis are carcinogenic to the liver. Bile acids, produced in the liver and metabolized by gut bacteria are hepatocarcinogenic in mice, and lipopolysaccharide (LPS, a component of bacterial membranes) leaking from the gut causes liver cancer in mice. Our preliminary data show that deoxycholic acid (DCA, a secondary bile acid and gut metabolite) and intestinal fatty acid binding protein (I-FABP, a marker of enterocyte damage and gut permeability) are elevated, while several other bile acids and immune markers are reduced, in the plasma of cirrhotics with HCC compared to cirrhotics without HCC. In prior prospective cohort studies, we have demonstrated that markers related to LPS exposure (e.g. sCD14) and chronic immune activation/inflammation (e.g. interleukin 6 & IFN?-induced protein 10) are elevated prior to the development of lymphoma in high risk HIV-infected populations by several years. In the proposed study, we will examine the contributions of bile acids, markers of LPS exposure, and immune response to LPS to HCC in a high-risk clinical cohort of 370 cirrhotic patients who are followed prospectively for HCC development. We will recruit study participants for two years from the large pool of patients awaiting a liver transplant at two large transplant centers in Los Angeles. We expect that approximately 40% of our study population will be Hispanic, which will allow us to examine pathways for HCC in the demographic group that is at the highest risk for HCC and stands to gain the most from the proposed research. Study participants will provide baseline duodenal aspirate fluid, peripheral blood specimens, epidemiological data, nutritional data, and consent to access their medical charts. Mid-way through year four, we expect that 56 cohort members will have developed HCC over the follow-up period. We will design a nested case-control study to include 56 HCC cases and 112 cirrhotic controls (matched 2:1), and measure 7 candidate bile acids and 14 immune markers in in paired blood (serum) and duodenal aspirate fluid specimens from these participants. We will test each marker individually, and with other clinical and epidemiological characteristics, for association with HCC using mixed effects logistic regression. The information gained from this study may open prospects for therapeutic interventions or new parameters for transplant prioritization that could delay or avert HCC in the cirrhotic patient.